Marine phytoplankton growth and survival under simulated upwelling and oligotrophic conditions

Abstract

Dialysis cultures of a diatom, Chaetoceros affinis Lauder, and a dinoflagellate, Gymnodnium splendens Lebour were subjected to simulated upwelling conditions which were followed by oligotrophy. Upwelling was simulated by pumping nutrient-enriched sea water past the enclosed cultures. Oligotrophy was simulated by pumping nutrient-poor sea water past the cultures. After the period of upwelling oligotrophy was carried on for 65 days for G. splendens and 80 days for C. affinis. Both algae survived oligotrophic conditions as evidenced by the ability to initiate new cultures or by observation of motility. Nutrient analyses showed that oligotrophy developed slowly — over a period of several days — so that the cultures were subjected to slow changes similar to those which might occur in the sea when upwelling ceases or when upwelled water moves offshore. C. affinis responded to oligotrophy by developing small flagellated cells (male gametes), by losing discrete protoplasts in silicified cells, and by the breaking up of normal chains of cells. Plastids in G. splendens cells became more discrete under oligotrophic conditions and some large non-flagellated cells were observed. The use of dialysis cultures to simulate features of the ocean is discussed.